The American man who was among the 14 people killed in an attack on a luxury hotel complex in the Kenyan capital Nairobi was a consultant who survived the 9/11 attacks, and specialised in emerging economies.

Authorities did not formally name Jason Spindler as one of the victims, but his mother Sarah and brother Jonathan confirmed his death on Facebook and to several US media outlets.

"It's with a heavy heart that I have to report that my brother, Jason Spindler, passed this morning during a terror attack in Nairobi," Jonathan wrote on Facebook, in comments visible only to his friends.

"Jason was a survivor of 9-11 and a fighter. I am sure he gave them hell!"

The Nairobi attack was claimed by the al-Qaeda-linked Somali group Al-Shabaab, which has targeted Kenya since it sent its army into Somalia in October 2011 to fight the jihadist group.

Spindler was a graduate of the University of Texas at Austin and the New York University law school. He spent time in the Peace Corps in Peru.

On September 11, 2001, Spindler was working for investment bank Salomon Smith Barney in the World Trade Centre.

The main Twin Towers collapsed after being hit by two passenger jets commandeered by Al-Qaeda operatives.

Spindler's building, 7 World Trade Center, collapsed in the aftermath, but none of the nearly 3,000 fatalities that day resulted from that incident.

He later co-founded consulting and investment firm I-Dev, and was working in Kenya on a mini-power grid project tailored for remote areas, according to the company's website.

His mother Sarah told NBC News that her son "was trying to make positive change in the third world in emerging markets."

"We all miss him so much. And it's so sad that such a bright young person is taken away by terrorism," she added.

Spindler's Facebook account had been converted on Wednesday into a tributes page.